A mold-type semiconductor laser forming a package constituted by a lead frame and a mold resin has a structure, for example, shown in FIG. 8. As shown in FIG. 8, a sub-mount 67 to which a laser (LD) chip 68 is bonded is installed on a die pad 62a at the tip of a common lead 62 of three leads 62, 63 and 64 that are integrally formed as a lead frame 61. This LD chip 68 and a monitor-use light-receiving element 65 are wire-bonded to the other leads 63 and 64 through wires, not shown. Further, as shown in FIG. 8, a frame member 66, which has been, for example, transfer molded by using a synthetic resin, is formed on the peripheral portion except for the beam radiating side so that it is integrally formed together with the respective leads 62, 63 and 64; thus, the respective leads 62 to 64 are secured even when they are separated from the lead frame 61.
In the case when the entire lower face of the lead frame is exposed, from the necessity of preventing short-circuiting between the adjacent leads 62 to 64 due to heat radiation from the die pad 62a upon being formed on an electric conductor or the like, and of firmly securing the leads 62 to 64 onto the frame member 66, resin is directed round to the rear-face side of the lead frame 61 so as to cover the leads 62 to 64 on the periphery thereof. In this case, however, since the die pad 62a is more easily allowed to dissipate heat when it is exposed, a down-set forming process in which the portion of the die pad 62a is lowered from the face of the lead frame 61 to be exposed is carried out, or an up-set forming process in which, without deforming the lead 62 of the die pad 62a, the tips of the leads 63 and 64 on both of the sides are bent upward is carried out, as shown in FIG. 8.
As described above, the conventional mold-type semiconductor laser has a structure in which the die pad rear face of the lead frame is exposed to form a flat face so that it is made in contact with a heat radiation plate and the like so as to dissipate heat. However, in the case when the down-set forming process or the up-set forming process in which the die pad is pressed downward from the frame surface or the tips of the other leads are pushed up is carried out, complex processes are required, and these processes tend to cause a return after the processes and a deformation due to contact with other members, making it difficult to control forming precision. Further, even a slight deviation in the forming shape tends to cause resin burrs upon molding, resulting in a failure in firmly making the die pad rear face in contact with the heat radiation plate to cause the subsequent insufficient heat radiation.
Moreover, the lead portion is often coated with resin, and since the die pad portion has a structure in which, as shown in FIG. 8, the resin is placed only on one face on the periphery thereof, the adhesive strength is weak with the result that the die pad tends to be raised from the resin portion to cause degradation in the wire-bonding reliability when the raised die pad is moved.
Furthermore, when assembled in a pickup, the semiconductor laser is placed in a housing or the like to be accurately positioned and also to allow heat dissipation, and in this case, since the resin portion is formed on the periphery of the die pad as the frame member, the positioning process has to be carried out on the resin portion; however, the resin portion fails to provide an accurate positioning process due to the occurrence of resin burrs and the like, and consequently to cause a failure in determining an accurate position as well as a failure in dissipating heat with the exposed portion of the die pad being firmly made in contact with the housing. In this case, even when the resin portion is made in contact with the housing, it is not possible to sufficiently radiate heat due to a poor thermal conductivity in the resin. In particular, along with the recent developments in data-writable CD-R/RWs and the like, there have been demands for higher-power semiconductor lasers, and those having a higher power ranging from a conventional level of 5 mW to not less than 200 mW are required, and the resulting problem is that the service life of the semiconductor laser would be shortened without efficient heat dissipation.
Moreover, along with the current developments in lighter, thinner and small-size electronic apparatuses, there have been demands for smaller-size pickups as well as demands for smaller-size semiconductor lasers, and it is, therefore, not possible to make the external shape larger so as to improve heat dissipation.